Specific derivatization methods reactions to alter structure

2 Specific Derivatization Methods Reactions to Alter Structure 

Acetylation is one of the most frequently used derivatization techniques in the mass spectral analysis of peptides. Reaction with freshly distilled acetic anhydride in methanol [27] results in acetylation of a-amino functionalities within one minute. Acetylation at other less reactive sites may be accelerated by the addition of a small amount of base, such as NaHC03 or triethylamine [28], Peptide hydroxyl and amino groups can be acety-lated by exposure to a 1 1 mixture of acetic anhydride/ pyridine for about 40 minutes. The net result of the reaction is a positive shift of 42 daltons for each acetyl group addition. The failure of an acetylation reaction in a peptide analysis may be diagnostic of a blocked N-terminus. 

N-Acetylation of a peptide is normally performed by adding a threefold excess of a 3 1 methanol/acetic 

In order to simplify further the identification of the N-terminus-containing ions. Hurt and Morris have suggested the use of stable isotopes [29]. If the N-acetylation of leucine-enkephalin is performed with a 1 1 mixture of and acetic anhydride in methanol, the mass spectrum of the product consists of doublets 

From these data one may easily locate the various N-terminus-containing and non-N-terminus-containing ions as shown below. 

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